Devices including, methods using, and compositions of reflowable getters

ABSTRACT

Methods for protecting circuit device materials, optoelectronic devices, and caps using a reflowable getter are described. The methods, devices and caps provide advantages because they enable modification of the shape and activity of the getter after sealing of the device. Some embodiments of the invention provide a solid composition comprising a reactive material and a phase changing material. The combination of the reactive material and phase changing material is placed in the cavity of an electronic device. After sealing the device by conventional means (epoxy seal for example), the device is subjected to thermal or electromagnetic energy so that the phase changing material becomes liquid, and consequently: exposes the reactive material to the atmosphere of the cavity, distributes the getter more equally within the cavity, and provides enhanced protection of sensitive parts of the device by flowing onto and covering these parts, with a thin layer of material.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of, and claims the benefit of priorityof, U.S. application Ser. No. 13/633,332, filed on Oct. 2, 2012, whichis a continuation of U.S. application Ser. No. 13/193,033, filed Jul.28, 2011, now U.S. Pat. No. 8,310,154, which is a continuation of U.S.application Ser. No. 11/845,719, filed Aug. 27, 2007, now U.S. Pat. No.8,013,526, which is a divisional of U.S. application Ser. No.10/606,726, filed Jun. 26, 2003, now abandoned, which claims the benefitof U.S. Provisional Application No. 60/457,404, filed Mar. 24, 2003. Thedisclosure of the prior applications are considered part of (and areincorporated by reference in their entirety in) the disclosure of thisapplication.

FIELD OF THE INVENTION

The invention relates generally to the field of microelectronicsfabrication. More particularly, the invention relates to gettering ofmoisture, oxygen and other harmful species in encapsulatedmicroelectronics devices.

BACKGROUND OF THE INVENTION

Microelectronics devices including Organic Light Emitting Diodes (OLEDs)contain thin layers of materials very sensitive to oxygen and moisture.These devices are typically encapsulated, and a getter is usually placedin the cavity of these devices. The getter can be a zeolite tablet orpowder, an oxide (BaO, CaO), or a reactive metal (such as Ba and itsalloys with other metals such as Al). Once the zeolites have beenactivated at high temperature, they must be handled and processed underrigorously dry conditions. Reactive metals and oxides must also behandled under controlled conditions so they do not react or lose theiractivity.

Various aspects of the invention will be better appreciated andunderstood when considered in conjunction with the following descriptionand the accompanying drawings. It should be understood, however, thatthe following description, while indicating preferred embodiments of theinvention and numerous specific details thereof, is given by way ofillustration and not of limitation. Many changes and modifications maybe made within the scope of the invention without departing from thespirit thereof, and the invention includes all such modifications.

BRIEF DESCRIPTION OF THE DRAWINGS

A clear conception of the advantages and features constituting theinvention, and of the components and operation of model systems providedwith the invention, will become more readily apparent by referring tothe exemplary, and therefore non-limiting, embodiments.

FIG. 1A illustrates placement of an activated powder and molten waxgetter composition within an encapsulated device prior to reflow,representing an embodiment of the invention.

FIG. 1B illustrates placement of an activated getter and molten waxgetter composition within an encapsulated device after reflow of thegetter composition, representing an embodiment of the invention.

FIG. 2A illustrates a prior art glass cap with a cavity.

FIG. 2B illustrates a glass cap including an active getter, according toan embodiment of the invention.

FIG. 2C illustrates a glass cap including an active getter and anadjacent binder layer, representing an embodiment of the invention.

FIG. 3A illustrates a microelectronics device assembly including the capof FIG. 2C, representing an embodiment of the invention.

FIG. 3B illustrates a microelectronics device assembly after the inertlayer has been removed from the active getter, representing anembodiment of the invention.

FIG. 4A illustrates the placement of a reflowable getter compositiononto a microelectronic device prior to encapsulation, representing anembodiment of the invention.

FIG. 4B illustrates a microelectronic device assembly with the gettercomposition after encapsulation, and sealing.

FIG. 4C illustrates a microelectronic device assembly after reflow ofthe getter composition so that the getter composition covers the entireactive area of the microelectronic device.

DESCRIPTION OF PREFERRED EMBODIMENTS

The invention and the various features and advantageous details thereofare explained more fully with reference to the embodiments that areillustrated in the accompanying drawings and detailed in the followingdescription of preferred embodiments. Descriptions of well-knowncomponents and processing techniques are omitted so as not tounnecessarily obscure the invention in detail.

The term coupled, as used herein, is defined as connected, although notnecessarily directly, and not necessarily mechanically. The termsubstantially, as used herein, is defined as approximately (e.g.,preferably within 10% of, more preferably within 1% of, most preferablywithin 0.1% of).

Methods for Protecting Circuit Device Materials

Some embodiments according to a first aspect of the invention provide amethod for protecting circuit device materials. Examples of theseembodiments are depicted in FIGS. 1A, 1B, 3A, 3B, 4A, 4B, and 4C. Themethod comprises mixing a reactive material 12A with a comparativelyinert material 12B to form a getter 12; placing the getter in the device10; applying energy to the getter; and responsive to applying theenergy, distributing the getter inside the device. The comparativeinertness is relative to the reactive material. For some embodiments asshown in FIG. 1B, a reflowed getter composition 22 covers an active OLEDarea 14. The reflowed getter composition can also be used to coveractive areas of other optoelectronic devices including light detectorarrays or solar cell arrays. The inert material 12B can comprise abinder. The placing can be accomplished by automated means.

In some embodiments, as depicted in FIGS. 1B, 3B and 4C, the method forprotecting circuit device materials further comprises sealing thedevice. For these embodiments, the device can comprise an optoelectronicdevice. The optoelectronic device can include a substrate 16 and anactive OLED area 14.

For some of these embodiments, placing the getter 12 can include placingthe getter on a surface of a cap 18, sealing the device includes joiningthe cap to the substrate. Distributing the getter 12 can includetransferring at least a portion of the getter to cover the active OLEDarea 14. Transferring at least a portion of the getter 12 to cover theactive OLED area 14 can include heating the getter to a temperature inthe range of 75 to 300 degrees Celsius, and can provide an encapsulateddevice after reflow of the getter 20 as shown in FIG. 1B. The portion ofthe getter 12 transferred to cover the active OLED area 14 can begreater than approximately eighty percent. The active OLED area 14 caninclude a central portion and a periphery. Distributing the getter 12can include covering at least 50% of the periphery of the active OLEDarea 14. The distributing can occur after final assembly of anencapsulated device before reflow of the getter 10 as shown in FIG. 1A.

Some embodiments according to a second aspect of the invention provide amethod for protecting circuit device materials. Examples of theseembodiments are depicted in FIGS. 3A and 3B. The method comprisesplacing a reactive material 12A on an interior surface of the device 10;placing a meltable material 12B upon the reactive material tosubstantially cover the reactive material; and in response to anapplication of energy to the meltable material, removing at least aportion of the meltable material, the removing exposing at least aportion of the reactive material. The circuit device can comprise anoptoelectronic device including an active OLED area 14. The removingstep can include heating the meltable material 12B to a temperature inthe range of 75 to 300 degrees Celsius. The removing step can furthercomprise covering substantially all of the active OLED area 14 with themeltable material 12B. The method can further comprise sealing thedevice.

The methods for protecting circuit devices according to some embodimentsof this invention provide more flexible handling of the getter 12 duringfabrication of optoelectronic devices. The comparative size and shape ofa getter 12 with respect to the size and shape of the encapsulatingcavity has an impact on the performance of the getter. and thuspotentially the degradation of the optoelectronic device. For example,for large area but very thin devices such as flat panel displays, thepermeation of water vapor and other potentially harmful gaseous speciesthrough the seal 19 may cause some non-uniform degradation of thedisplay at the periphery of the device if the getter 12 is placed onlyat the center of the device. The present invention enables modificationof the shape and activity of the getter 12 after sealing of the device.

Optoelectronic Devices

Some embodiments according to a third aspect of the invention provide anoptoelectronic device. Examples of these embodiments are depicted inFIGS. 1B, 3B and 4C. The optoelectronic device comprises a substrate 16;an active device area placed on the substrate; and a getter 12. Thegetter 12 includes a first material 12B and a reactive material 12A. Thefirst material 12B can be adapted to respond to energy input by at leastone of: melting, phase change, or morphological change. An example ofthe active device area is shown in FIG. 3B as an active OLED area 14.

The optoelectronic device can further comprise a seal 19 joining thesubstrate 16 to a cap 18. The at least one of: melting, phase change,and morphological change can result in reflowing of the first material12B. Prior to the reflowing, the getter 12 can be disposed on a recessedsurface of the cap 18. After the reflowing, the getter 12 can bedisposed to cover a substantial portion of the active OLED area 14.

The first material 12B can comprise at least one of paraffin wax,low-density polyethylene, or Elvax□ resin. Alternatively, the firstmaterial 12B can comprise a binder, and the reactive material 12A can besubstantially dispersed within the binder.

Cap

Some embodiments according to a fourth aspect of the invention provide acap 18 for enclosing an optoelectronic device. Examples of theseembodiments are depicted in FIG. 2C. The cap 18 comprises a reactivematerial 12A disposed on a cap surface; and an inert material 12B placedto cover more than approximately fifty percent of the reactive material.The inert material 12B can be adapted to flow in response to applicationof energy to the inert material. The cap 18 can include an interiorsurface having a recessed portion. The inert material 12B can cover atleast some of the recessed portion. In response to the application ofenergy, the inert material 12B can melt. The inert material 12B cancover less than the entire recessed portion thereby leaving a cavitybetween the inert material and at least one sidewall 18D of the recessedportion.

Getter Composition

Some embodiments according to a fifth aspect of the invention provide agetter composition. Examples of these embodiments are depicted in FIGS.1B, 2C, 3A, and 4C. As shown in FIG. 1B, the reflowable gettercomposition 12 can be formed as a reactive material 12A dispersed withinan inert binder 12B. As shown in FIG. 2C, the getter composition cancomprise: a reactive material 12A disposed in an encapsulated device 10,and an inert material 12B disposed in the encapsulated device. Thereactive material 12A is more reactive than at least one device materialto desorbed matter and matter from a space within the device. Thedesorbed matter can be desorbed from at least one of: a substrate, afilm disposed upon the substrate, and an encapsulation surface. Theinert material 12B can be adapted to respond to energy input by at leastone of: melting, phase change, or morphological change. The reactivematerial 12A can comprise an activated powder containing at least one ofactivated alumina, silica, zeolite, barium oxide, calcium oxide,calcium, and barium. The inert material 12B can comprise at least one ofparaffin wax, low-density polyethylene, or Elvax® resin. The inertmaterial 12B can comprise a binder, and the reactive material 12A, e.g.activated powder can be mixed with the binder so that the reactivematerial is substantially dispersed in the binder.

In some embodiments, the inert material 12B responds to energy input bymelting. Upon removal of the energy, the inert material 12B solidifies.In some of these embodiments, each device material is adapted to provideenhanced performance of an optoelectronic device.

Preparation of the Getter

Preparation of the getter according to some embodiments of theinvention, as exemplified in FIGS. 1A, 1B, 1C, 4A, 4B and 4C, is asfollows:

A getter 12 comprised of an reactive material 12A (activated powder)mixed with a inert material 12B (binder) is selected to provide anequilibrium minimum humidity level lower than a humidity level to whichthe OLED device is sensitive when sealingly enclosed by an enclosurecontaining the getter;

The activated powder can have a particle size range of about 0.1 toabout 200 micrometers.

The binder can be chosen for dispersing the selected activated powdertherein. The inert material 12B (binder) can be chosen from variousclasses of materials so that the binder can have a low moistureabsorption rate; e.g., if the binder is selected from non polarhydrocarbons such as waxes, paraffins, polyolefins. Alternatively, theinert material 12B (binder) can have a higher moisture absorption rateif selected from more polar materials such as low molecular weightacrylates, polyurethanes, polyamides. During reflow of the inertmaterial 12B, the moisture absorption rate of the binder may change.

The inert material 12B can be selected so that a blend can be formed ofthe reactive material 12A (activated powder) and the inert material 12B(e.g., wax) in a preferred weight fraction of the activated powder inthe blend in a range of approximately 10% to 90%.

A measured amount of the getter 12 blend can then be applied on aportion of the upper interior surface of a glass cap 18 by dispensing ameasured amount of the getter 12 blend above the blend's melting pointwith a heated syringe dispensing system until the dispensed blend hasspread along the interior surface to form a reflowable getter layer 12.However, because the blend can be re-melted after final assembly of thedevice, the dispensed blend can have any shape (such as a droplet), sothat there is no need to initially dispense the blend uniformly onto thesurface of the enclosure. The layer is then cooled to about roomtemperature until it solidifies to form a solid getter 12 layer, so thatthe getter layer has the desired getter layer thickness (t) and coversthe desired surface. Alternatively, the getter 12 composition can beshaped as a thin pellet whose shape and dimension are such that thepellet can fit in the cavity of the device to be protected, and thispellet can be placed inside the device cavity. The pellet can be placeddirectly on top of the active OLED area 14, or in the cap 18. Theplacement can be accomplished either manually or through use ofautomatic pick-and-place equipment.

The preparation of the getter 12 according to other embodiments of theinvention, as shown in FIGS. 2C, 3A, and 3B, is as follows:

A reactive material 12A, e.g., an active getter, is selected to providean equilibrium minimum humidity level lower than a humidity level towhich the device is sensitive when sealingly enclosed by an enclosurecontaining the active getter.

The reactive material 12A can be a reactive metal such as barium.Reactive material 12A can be deposited onto the cap 18 by physical vapordeposition techniques, e.g., thermal evaporation or sputter deposition;or by chemical vapor deposition techniques. For some embodiments,reactive material 12A can be a finely-divided powder of a reactive metalor an alkaline metal oxide and has a preferred particle size range ofabout 0.1 to about 200 micrometers. In some embodiments the particlesize range is from 0.3 to 50 micrometers.

A meltable inert material 12B, e.g., a molten wax, can be chosen forcoating the reactive material 12A before reflow, and for coating theactive OLED area 14 after reflow.

A measured amount of the reactive material 12A can be applied on aportion of the recessed interior surface of the cap 18, for example byevaporation of a reactive metal, until the reactive material 12A hasformed a layer along the desired area of the recessed portion of theinterior surface of the cap. Prior to placement of the reactive material12A on the cap 18, the cap has a pre-getter placement cavity 18A. Insome embodiments the portion of the recessed interior surface covered bythe reactive material 12A is in a range of 25% to 90%. Depending on thepermeation rate of the seal 19, the permeation rate of the inertmaterial 12B, the reaction rate of the reactive material 12A, and thereaction rate of the active area 14 to be protected, the portion of theinner surface covered by the reactive material 12A can be in the rangeof 10% to 99%. As shown in FIG. 2C and FIG. 3A, a volume of spaceunderneath the cap after application of reactive material 12A is boundedby a cap sidewall 18D and the lateral extent of the inert material 12B,and is referred to as the pre-reflow cavity 18B. As shown in FIG. 3B,inert material 12B has transferred to the active OLED area 14, theremaining reactive material 12A extends towards the sidewall 18D, andthe volume of space underneath cap is referred to as the post re-flowcavity 18C. In some embodiments, the reactive material 12A layer has athickness in the range of about 0.1 micron to 10 microns.

Under controlled conditions (e.g., low moisture atmosphere) a measuredamount of inert material 12B, e.g., meltable material, is then placedupon the reactive material 12A (active getter). The meltable inertmaterial 12B covers substantially all of the reactive material 12A, andin some embodiments also extends to cover a portion of the recessedportion of the interior surface of the cap 18. Typically, the meltableinert material 12B does not cover the entire length of the recessedportion of the interior surface. Once the reactive material 12A has beencovered with the meltable inert material 12B, the active getter layerbecomes much less susceptible to deactivation by ambient conditions(i.e., the active getter layer is less susceptible to loss of getteringcapacity due to reactions with ambient gases), and thus the caps can beeasier to handle in a mass production process. The reactive material 12Acan be uncovered by melting and displacing the meltable inert material12B as needed to regain its gettering function.

EXAMPLES

Specific embodiments of the invention will now be further described bythe following, non-limiting examples which will serve to illustrate insome detail various features of significance. The examples are intendedmerely to facilitate an understanding of ways in which the invention maybe practiced and to further enable those of skill in the art to practicethe invention. Accordingly, the examples should not be construed aslimiting the scope of the invention.

Example 1

As shown in FIGS. 1A and 1B, a reflowable getter composition 12 can bemade (under controlled conditions, e.g, using a glove box where theoxygen and moisture concentration can be reduced to a very low levelwhen mixing a reactive material 12A (e.g., activated powder) with aninert material 12B (e.g., molten wax). The activated powder 12A can beactivated silica gel, alumina, activated zeolite powder, barium oxide(BaO) or other alkaline earth metal oxides, or barium (Ba) powder orother alkaline metals or alkaline earth metals. The inert material 12Bcan be natural or synthetic waxes, paraffin waxes, microcrystallinewaxes, polyolefin resin waxes such as polyethylene, polypropylene,polybutene, polyethylene oxide, polypropylene oxide and their copolymerssuch as Elvax® resin from DuPont; ester waxes, polyurethane waxes,silicone resin waxes. The getter composition 12 can be shaped as a thintablet and placed into the enclosure of the device to be protected, suchas encapsulated device before reflow 10.

The encapsulated device before reflow 10 is then sealed. In someembodiments as shown in FIG. 1A, the sealed encapsulated device beforereflow 10 includes: reflowable getter composition 12, an active OLEDarea 14, an OLED substrate 16, a glass cap with a cavity 18, and atleast one epoxy seal 19.

Upon further processing, for example heating, the reflowable gettercomposition 12 can melt and distribute itself evenly inside the deviceto form an encapsulated device after getter reflow 20, as shown in FIG.1B. In some optoelectronic devices where the thickness of the cavity isvery small compared to the width and length of the device such as a flatpanel display, it may be preferable that the getter material beuniformly distributed on the entire inner surface of the device. It hasbeen observed that the shape of the getter material is important toprotect such a display from degradation. If the getter material isplaced in the center of the display, some degradation is observed on theperiphery of the active area of the display. If the getter compositioncan be melted so that it distributes itself evenly inside the cavity,the periphery of the active layers of the display will be betterprotected since any moisture of oxygen permeating inside the devicethrough the epoxy seal on the periphery will react first with the gettermaterial.

Example 2

According to some embodiments of the invention and as shown in FIG. 2B,an reactive material 12A can be deposited (by evaporation or othermeans) onto a glass cap 18. The active getter can be a reactive metal,such as barium. As shown in FIG. 2C, the reactive material 12A can thenbe protected with a thin film of a metlable inert layer 12B, such asparaffin wax, so that the cap 18 can be manufactured and handled easily.

As shown in FIGS. 3A and 3B, the cap 18 can then be used to encapsulatea device, using an epoxy seal 19 or other conventional means. Theassembly is then subjected to thermal, or other, energy so that themetlable inert layer 12B melts, exposing the reactive material 12A tothe atmosphere of the device on the one hand, and further protecting theactive parts of the device by covering the inside of the device with athin layer of wax, as shown in FIG. 3B.

Preparation and Sealing of OLEDs with Reflowable Getters

The reflowable getter 12 can be advantageously used in the production ofOLEDs. An appropriate amount of the getter 12 composition as describedin Example 1 can be dispensed as a hot liquid onto a glass or a metalcap 18 with a heated syringe and cooled down to room temperature so thatthe liquid getter composition solidifies. The substrate 16 having theactive OLED area 14 can then be sealed with this cap 18 using a sealantsuch as a UV-curable epoxy adhesive. Once cured, the OLED assembly canbe heated above the melting point of the inert material 12B(wax/binder), thus causing the reflowable getter composition to flowinside the entire inner cavity, and evenly distributing the getterparticles inside the device cavity. For some embodiments, the inertmaterial 12B (e.g., wax or binder) can wet and spread itself inside thedevice cavity because of the inert material's low surface tension,especially where the getter 12, in its molten state, is reasonably fluidand does not behave as a thixotropic liquid. In addition, the inertmaterial 12B (e.g., wax) can provide additional protection to the activeOLED area 14.

Alternatively, the reflowable getter 12 can be placed (as a liquiddroplet or as a solid tablet) directly on top of the active OLED area14, as shown in FIG. 4A. The cap 18 can then be placed onto the OLEDdevice with the appropriate sealant such as a UV-curable epoxy. For someembodiments, the sealing surfaces in contact with the sealing materialare preferably very clean and not contaminated with materials used inthe manufacturing process of the active OLED area, such as photoresists,solvents, or organic light emitting materials. Typically, the sealingarea is cleaned by an ablation process just before encapsulation. Afterassembly and sealing of the device, the reflowable getter 12 can beheated above its melting point, causing the getter to flow inside thecavity up to the edge of the sealing area. Such edge coverage isotherwise difficult to achieve without the risk of contaminating thesealing area.

The effectiveness of a getter 12 in an OLED device can be evaluated bymeasuring the dimensions of the light emitting areas (pixels) afterexposure to a testing environment, with respect to the initial lightemitting areas. Typically, the shrinkage of the light emitting areas ismore severe at the periphery of the OLED display, close to the sealingarea, especially when the getter is placed at the center of the cap.Uniformly reflowing the getter 12 inside the OLED cavity, provides moreuniform shrinkage of the light emitting areas. In addition, the inertbinder material 12B provides additional protection to the active OLEDarea, in the case where the inert binder material has been reflowed overthe active OLED area 14, as shown in FIGS. 3B and 4C.

Various additions, modifications and rearrangements of the features ofthe invention may be made without deviating from the spirit and scope ofthe underlying inventive concept. It is intended that the scope of theinvention as defined by the appended claims and their equivalents coverall such additions, modifications, and rearrangements. The appendedclaims are not to be interpreted as including means-plus-functionlimitations, unless such a limitation is explicitly recited in a givenclaim using the phrase “means-for.” Expedient embodiments of theinvention are differentiated by the appended subclaims.

1. A cap comprising a getter, the cap further comprising: a reactivematerial disposed on a cap surface; and an inert material that coversmore than approximately fifty percent of the reactive material, whereinthe inert material is adapted to flow in response to application ofenergy to the inert material.
 2. The cap of claim 1, wherein the capcomprises an interior surface having a recessed portion.
 3. The cap ofclaim 2, wherein: the inert material covers at least some of therecessed portion; and the inert material is adapted to melt in responseto the application of energy.
 4. The cap of claim 2, wherein the inertmaterial covers less than the entire recessed portion, and wherein acavity is positioned between the inert material and at least onesidewall of the recessed portion.
 5. A device comprising a capcomprising a recessed portion; and a getter comprising an inert materialand a reactive material, wherein the inert material is adapted torespond to energy input by undergoing at least one of a phase change anda morphological change; and wherein the getter is at least partiallyarranged in the recessed portion.
 6. The device of claim 5, wherein thephase change comprises melting.
 7. The device of claim 5, wherein theinert material and the reactive material form two separate layers of thegetter.
 8. The device of claim 5, wherein the recessed portion comprisesan interior surface, and wherein between 25% and 90% of the interiorsurface is covered by the reactive material.
 9. The device of claim 5,wherein the recessed portion comprises a pre-reflow cavity which is freeof the getter.
 10. The device of claim 5, wherein the reactive materialis formed as a layer having a thickness in a range from 0.1 micrometersto 10 micrometers.
 11. The device of claim 5, wherein: the recessedportion comprises an interior surface; the inert material completelycovers portions of a surface of the reactive material that are notcovered by the cap; and the inert material covers a portion of theinterior surface.
 12. The device of claim 5, wherein: the reactivematerial comprises particles of a reactive metal or an alkaline metaloxide; and sizes of the particles are in a range from about 0.1micrometers to about 200 micrometers.
 13. The device of claim 12,wherein the sizes of the particles are in a range from about 0.3micrometers to about 50 micrometers.
 14. The device of claim 5, wherein:the getter comprises a blend of the reactive material and the inertmaterial; and a weight fraction of the reactive material in the blend isin a range from 10% to 90%.
 15. The device of claim 5, wherein the capcomprises a glass material.